1. Field of the Invention
The present invention relates to a solid-state imaging device, an imaging device and a driving method of the solid-state imaging device. More particularly, the present invention relates to a pixel driving technique suitable for semiconductor devices such as solid-state imaging devices for detecting physical quantity distribution and other electronic equipment which include an arrangement of a plurality of unit pixels sensitive to externally fed electromagnetic waves such as light and radiation, and from which a physical quantity distribution, converted into an electric signal by unit components, can be read out in the form of an electric signal through arbitrary selection by address control.
2. Description of the Related Art
Semiconductor devices for detecting physical quantity distribution have found wide application in a variety of fields. Such devices have a plurality of unit components (e.g., pixels), sensitive to externally fed electromagnetic waves such as light and radiation, arranged in lines or in a matrix form.
In the field of video equipment, for example, CCD (Charge Coupled Device) or MOS (Metal Oxide Semiconductor) and CMOS (Complementary Metal Oxide Semiconductor) solid-state imaging devices are used. These devices are designed to detect light (an example of electromagnetic waves) among other physical quantities. Such devices allow a physical quantity distribution, converted into an electric signal by unit components (pixels in a solid-state imaging device), to be read out therefrom in the form of an electric signal.
Some solid-state imaging devices are amplifying devices. These devices include, in a pixel signal generation section, pixels configured as solid-state imaging elements (APSs: Active Pixel Sensors, also referred to as gain cells), each of which has an amplifying drive transistor. The pixel signal generation section generates a pixel signal commensurate with the charge of the signal generated by a charge generation section. For example, many of CMOS solid-state imaging devices are configured in such a manner.
In order to read out a pixel signal externally from such an amplifying solid-state imaging device, a pixel section having an arrangement of a plurality of unit pixels is address-controlled so that the signal from a unit pixel can be arbitrarily selected and read out. That is, an amplifying solid-state imaging device is an example of address-controlled solid-state imaging device.
In an X-Y address solid-state imaging device having unit pixels arranged in a matrix form, MOS transistors serve as active elements such as switching elements adapted to select pixels and read out signal charges. Further, MOS transistors are used in horizontal and vertical scan circuits, offering an advantage in that both the switching elements and pixel section can be manufactured in a series of steps.
A unit pixel includes a charge generation section and signal output section. The charge generation section generates a signal charge. The signal output section has a transistor adapted to generate and output a target signal which is commensurate with the signal charge generated by the charge generation section. For example, the charge generation section has a photodiode which performs photoelectric conversion. The signal output section has a readout selection transistor, amplifying transistor, reset transistor and selection transistor. The readout selection transistor reads out the signal charge generated by the photodiode. The amplifying transistor converts the read signal charge into a pixel signal. The reset transistor resets the signal charge. The selection transistor selects the pixel to be read out. The signal charge (photoelectron or hole) accumulated in the photodiode, a photoelectric conversion element, is amplified by the active elements of the signal generation section and read out as image information.
Incidentally, electronic exposure time control is performed in this type of solid-state imaging device. In the imaging device, the pixel section includes a number of pixel transistors arranged two-dimensionally in a matrix form. The accumulation of signal charge associated with incident light begins on a pixel-by-pixel or line (row)-by-line (row) basis. The current or voltage signals based on the accumulated signal charge are read in order from the pixels in a imaging section through address specification. In a broad sense, this is called electronic shutter function. Here, a pixel signal is read out from the pixel section on a row-by-row basis by accessing a row of pixels at the same time. This example of address control (hereinafter referred to as row-by-row readout or column readout scheme) is common in a MOS (including CMOS) solid-state imaging device.
It should be noted that, in some X-Y address solid-state imaging devices, unnecessary signal charge of a row of pixels is reset (discharged to a signal line), for example, during a horizontal blanking period in which no signal charge is read out, in order to achieve an electronic shutter function in a narrow sense. This electronic shutter function electronically specifies an exposure time different from a normal exposure time.
In an X-Y address solid-state imaging device, the time corresponding to the exposure time for the electronic shutter speed, i.e., the pixel accumulation time, is determined by the period of time from the discharge to the readout of the signal charge. Therefore, the accumulation and sequential readout scheme is used which reads out a pixel signal every pixel exposure time (accumulation frame time).
For example, when a CMOS solid-state imaging device is used, a pixel generally begins again, according to its operation principle, to accumulate signal charge obtained through photoelectric conversion from the moment when it outputs a signal. Therefore, the accumulation period deviates according to the scan timing of the imaging surface. That is, the accumulation time deviates by scan time from one scan line to another, resulting in so-called line exposure. Unlike a CCD (charge-coupled device) solid-state imaging device, global exposure is not used. Global exposure reads out the signal charges simultaneously from all the pixels to the vertical CCD by accumulating incident light on the photoelectric conversion elements during the same time period in the form of signal charges, thus satisfying the simultaneity condition for accumulation. Because a drive pulse is supplied row by row, line exposure (also referred to as rolling shutter or focal plane accumulation) is used in a CMOS solid-state imaging device, which is a significant difference from its CCD counterpart based on the accumulation and simultaneous readout scheme, that is, global exposure.
When the shutter speed is slow and a sufficiently long pixel accumulation time is specified, the deviation in accumulation period is negligible. However, if the shutter speed is fast and not much different from the horizontal scan period, the difference in accumulation period gives rise to time shading distortion in the line direction (row direction or horizontal scan direction) due to the horizontal motion of the object and the difference in scan time (accumulation period). Time shading distortion manifests itself in the form of a motion distortion on the image.